This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Streptococcus mutans is a known etiological agent in dental caries. The surface proteins on bacteria play a pivotal role in adhesion to tooth surface, and therefore they become important targets for development of preventative therapeutics. Antigen I/II is one such surface protein on S. mutans, whose importance has been well documented for the last 30 years. In this project, we elucidated both the functional regions, and their respective structures.